Priority Encoder

A priority encoder provide n bits of binary coded output representing the position of the highest order active input of 2n inputs. If two or more inputs are high at the same time, the input having the highest priority will take precedence.

It's applications includes

4 to 2 priority encoder

A 4-to-2 priority encoder takes 4 input bits and produces 2 output bits. In this truth table, for all the non-explicitly defined input combinations (i.e. inputs containing 2, 3, or 4 high bits) the lower priority bits are shown as don't cares (X). Similarly when the inputs are 0000, the outputs are not valid and therefore they are XX.

From the above truth table, we can obtain the full truth table required for our design.

From this truth table, we use the Karnaugh Map to minimise the logic to the following boolean expressions:

  • O1 = I2 + I3
  • O0 = ~I2 * I1 + I3

Implementation of the 4 to 2 priority encoder using combinational logic circuits.

Learn by Doing

Design a 4 to 2 Priority Encoder to deepen your understanding of the circuit.

Thank you for learning from

We do not have a paywall as our mission is to provide everyone from Albania to Zimbabwe, rich or poor, a quality foundational electronics education. With advertising revenues falling despite increasing numbers of learners, we need your help to maintain and improve the course, which takes time, money and hard work.

If everyone who benefits from this course gives as little as $2 via Paypal, we can continue to achieve our mission. Thanks!

Support Our Mission